The objective of this research is to measure in a species of new world primate time dependent, visual memory processes (length of retention interval) as well as mnemonic storage capacity (number of items to be remembered, or list length). Two kinds of memory will be studied: simple visual object recognition and complex stimulus-reward association. Two groups of squirrel monkeys will be initially trained to criterion on a trial-unique visual delayed (10 sec) match-to-sample task or on a visual delayed non-match-to-sample task. The group's acqusition rates will be compared to determine if, like old world monkeys, squirrel monkeys tend to respond preferentially to novel visual stimuli. In two subsequent experiments the accuracy of object recognition memory will be measured as a function of number of items (1,3,5,10) to be remembered as well as a function of length of retention interval (from several seconds to over 24 hours). Finally, the animals will be trained on a somewhat more complex stimulus-reward association task and this associative memory also will be measured as a function of list length and retention interval.